Alkaline-earth metal salts of alkylbenzene sulfonic acids find many commercial uses, including use as additives in lubricating oils; as corrosion inhibitors, in anti-freeze formulations for example; in rust-proofing compositions, in drilling mud formulations, and the like. As is obvious, these materials find many large volume uses and cost becomes an important factor. Manufacturing methods for preparing such materials are described in many patents. Generally alkylbenzene sulfonic acids are reacted with calcium hydroxide in an aqueous-organic solvent, and thereafter the water and most of the solvents are removed by distillation. Typical are U.S. Pat. Nos. 3,719,596 and 2,799,784.
In U.S. Pat. No. 3,719,596 there is described a method of preparing alkaline-earth alkylbenzene sulfonates. The process comprises forming a suspension of an alkaline-earth metal hydroxide with a water-immiscible azeotrope-forming liquid such as toluene, xylene, tetrachloroethylene or the like, and water, adding thereto a higher alkylbenzene sulfonic acid in a sufficient amount to form the double salt, lowering the pH to an acidic range thereby neutralizing the hydroxide, adding a lower alkanolamine having from 1 to 3 hydroxy groups such as diethylanolamine to neutralize the system and solubilize the salt, and finally, removing practically all of the water by distillation in the presence of a polyhydric alcohol such as ethylene glycol. Monohydric alcohols such as isopropanol are taught to be in appropriate for this use.
There is disclosed in U.S. Pat. No. 2,779,784 a method for making alkaline earth metal sulfonates by heating a mixture of an oil-soluble alkaryl sulfonic acid and an alkaline earth metal compound, preferably in the presence of a solvent, with water at a temperature above 220.degree. F. to 390.degree. F. and under superatmospheric pressure, and removing the water by azeotropic distillation. The alkaline earth metal compound to neutralize the sulfonic acid includes alcholoates, borates, carbonates, carboxylate, hydroxides, hydrates, hydrosulfide, oxides, nitrate, sulfide, thiocarbonates, and others of magnesium, calcium, strontium and barium. The water used is present in amount equal to 5 (50%) to 100 parts per 10 parts of alkaline earth metal compound. The patent teaches that "When an organic sulfonic acid and an alkaline earth metal compound in excess of that required to neutralize the sulfonic acid are agitated together in the presence of an appreciable amount of water at a temperature above 220.degree. F., and under sufficient pressure to hold the water in the liquid state, the water provides a condition whereby the excess alkaline earth metal compound forms a stable dispersion. If the reaction is carried out in an open kettle, the water escapes before the reactants reach the temperature at which dispersion of the alkaline earth metal compound is most suitably obtained."
In U.S. Pat. No. 4,279,837, the alkyl benzene sulfonic acids are neutralized with the necessary amount of basic alkaline earth metal compound in an inert organic solvent in the presence of 1 to 10% by weight of a oxalkylate, and the mixture is then azeotropically distilled to remove the water and a large part of the organic solvent.
A less complex and less costly process for making solutions of alkaline earth metal salts of alkaryl sulfonic acids having a low water content is desired. The elimination of a costly azeotropic distillation step is particularly desirable since this would make possible the elimination of costly equipment, some reagents, waste storage, and disposal, would use less energy, and would result in more efficient use of of existing facilities.